<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .red{
            background: red;
        }
        .font{
            font-size: 40px;
        }
    </style>
</head>
<body>
<div id="app">
<p :class="{red:isRed,font:isFont}">rrrrrrrrrr</p>
<p  :class="[classA,classB]">ppppp</p>
<p :class="classObj">fffffffff</p>
</div>
</body>
<script src="https://cdn.bootcss.com/vue/2.2.2/vue.min.js"></script>
<script>
    var vm = new Vue({
        el:"#app",
        data:{
            p:'p1111',
            pp:'sdadsdsss',
            isRed:false,
            isFont:true,
            classObj:{
                red:true,
                font:false
            },
            classA:'red',
            classB:'font'
        }
    })
</script>
</html>